This invention relates to a cylinder head gasket including a metal base plate which is provided with at least one combustion chamber opening and a metal annular overlay. The latter surrounds the combustion chamber opening and is welded to the base plate by a series of weld dots configured such that on one surface of the base plate the weld dot diameter is smaller than the weld dot diameter on a surface of the overlay.
At the edge region of the combustion chamber openings of conventional cylinder head gaskets upstanding portions constituted by metal overlays (annular metal disks) are arranged which function as pressure limiting devices for beads provided in the base plate and surrounding the combustion chamber openings. By using such overlays, a high pressure may be produced by the securing bolts which tighten the cylinder block and the cylinder head together, without fully flattening the base plate beads.
Such a cylinder head gasket is described, for example, in European Published Patent Application 0 468 526. Each annular disk (overlay) is, as a prefabricated component, held on the base plate of the gasket by means of a jig and is subsequently bonded to the base plate with a continuous weld seam by means of laser welding.
A welding of thin overlays to the metal plate in the above-outlined conventional manner involves the danger that excessive heat energy is introduced into the metal plate, causing deformation of both the overlays and the metal base plate.
To ensure that only a small amount of heat is introduced into the components, Published European Patent Application 0 468 817 discloses the formation of the weld seam by overlapping weld dots. The overlap seeks to ensure a gas tight bond, similarly to a continuous weld. In case of extremely thin overlays, having, for example, a thickness of less than 120 micron, risks are high that the surface of the overlay is damaged by the overlapping weld dots because the heat energy is excessively high.
It is an object of the invention to provide an improved cylinder head gasket of the above-outlined type in which extremely thin overlays may be used without adversely affecting the sealing function.
This object and others to become apparent as the specification progresses, are accomplished by the invention, according to which, briefly stated, the cylinder head gasket includes a metal base plate; a combustion chamber opening provided in the base plate; a metal overlay surrounding the opening; and a weld bonding the overlay to the base plate. The weld is composed of a plurality of weld dots lying in a single row and being equidistantly spaced from one another. Each weld dot has a first diameter on a surface of the base plate and a second diameter on a surface of the overlay. The first diameter is smaller than the second diameter, and a distance between center points of adjoining the weld dots is greater than the second diameter of either of the adjoining weld dots.
The weld seam according to the invention is formed by individual weld dots spaced from one another such that they do not overlap. In this manner, less heat energy is introduced thus avoiding a deformation of the overlay. Although the weld seam, in contrast to conventional cylinder head gaskets, is not closed in the circumferential direction, it has been found that such a circumstance has no adverse effect on the sealing function.
It has been found that it is even sufficient to select the distance between two weld dots such that only two weld dots are arranged about a combustion chamber opening.